Rule 901.6 · Planechase

The owner of a plane or phenomenon card is the player who started the game with it in their planar deck. The controller of a face-up plane or phenomenon card is the player designated as the planar controller. Normally, the planar controller is whoever the active player is. However, if the current planar controller would leave the game, instead the next player in turn order that wouldn’t leave the game becomes the planar controller, then the old planar controller leaves the game. The new planar controller retains that designation until they leave the game or a different player becomes the active player, whichever comes first.